This invention pertains to a sealant composition adapted to be used in sealing a can end to a can body of the type used for beverages, fruits, vegetables. aerosol cans, and a variety of commercial products, such as paints and automotive specialties. The attachment of ends to can bodies, either the drawn and ironed 2-piece cans or the 3-piece cans where ends are placed on each end of a cylinder, is well known in the art by an operation known as double seaming. The sealant is placed in the trough of a can end and attached to the can end by spinning an end under a fixed nozzle carrying a liquid sealant composition. Before the ends can be used, the liquid composition must "set" to a solid by either a change in temperature or by removal of volatiles.
Generally, the choice of a particular sealant composition can depend on the nature of the product to be packaged, although for the most part, all such sealant compositions are based on rubber dispersions compounded for performance on high speed equipment. Usually sealant compositions for can ends are classified into two groups, i.e. (1) water-based dispersions and (2) volatile organic-based rubber dispersions, the latter often being subdivided into: (a) those which are water resistant and are utilized in the packaging of fruits, vegetables, beverages and certain pet foods, and (b) those which are oil-resistant and are employed in the packaging of fish, poultry, soups and other meat products.
I have observed that can ends lined with a water-based rubber dispersion sealant composition are generally subjected to a separate drying operation to remove the water, whereas can ends lined with a volatile organic solvent-based dispersion sealant composition generally dry by themselves through the evaporation of the volatile solvents component while being stored in a work area or in a warehouse prior to their use.
Thus, while can ends lined with a volatile organic solvent-based rubber dispersion sealant composition provide an advantage over water-based compositions in that a separate drying operation may not be required; nonetheless, the use of volatile organic solvent-based compositions suffers from the disadvantage that the evaporation of large volumes of volatile organic solvents into populated areas where can plants are typically located causes undesirable air pollution as well as fire and health hazards. For example, in a typical daily operation, approximately 600 drums of such volatile organic solvent-based sealant compositions are employed, the average solvent content thereof being about sixty percent.
More specifically, one extensively employed volatile organic solvent-based rubber dispersion sealant composition is a hexane dispersion of SBR and/or butyl rubber, compounded with inert fillers, colors, aging stabilizers, viscosity stabilizers, and food grade antioxidants. The total solids content of such a sealant composition is about forty percent, the remainder being the volatile solvents component.
The use of this particular sealant composition can thus amount to about 19,800 gallons of volatile organic solvent per day, or just under five million gallons per year based on a 250 day work year, being exhausted to the surrounding atmosphere. Obviously, any significant reduction in the emission of such organic solvents to the environment is highly desirable. I have found that the use of the sealant composition of the present invention achieves this desideratum.